Variable compression ratio engines and methods for HCCI compression ignition operation

ABSTRACT

Variable compression ratio engines and methods for homogeneous charge, compression ignition operation. The engines effectively premix the fuel and air well before compression ignition. Various embodiments are disclosed including embodiments that include two stages of compression to obtain compression ratios well above the mechanical compression ratio of the engine cylinders for compression ignition of difficult to ignite fuels, and a controllable combustion chamber volume for limiting the maximum temperature during combustion. Energy storage with energy management are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/889,546 filed Feb. 6, 2018, which is a continuation of U.S. patentapplication Ser. No. 14/468,589 filed Aug. 26, 2014, which is acontinuation of International Application No. PCT/US2013/028088 filedFeb. 27, 2013 which claims the benefit of U.S. Provisional PatentApplication No. 61/603,818 filed Feb. 27, 2012, U.S. Provisional PatentApplication No. 61/608,522 filed Mar. 8, 2012 and U.S. ProvisionalPatent Application No. 61/663,996 filed Jun. 25, 2012.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to the field of compression ignitionengines.

2. Prior Art

Compression ignition engines are well known in the prior art. While suchengines can potentially operate on a wide range of liquid and gaseousfuels, commercially available compression ignition engines are limitedto operation on diesel fuel and biodiesel fuels. Historically, dieselengines emitted substantial quantities of unburned hydrocarbons andNO_(X). Such emission levels are no longer considered acceptable.Accordingly, recent developments have been incorporated to clean up theexhaust of diesel engines so that the same are competitive withcurrently available gasoline engines. However, adoption of alternatefuels for compression ignition engines has heretofore not succeeded, notbecause compression ignition cannot be achieved but because compressionignition is very difficult to achieve, and when achieved, the pressureand temperature spike that results raises the temperature in thecombustion chamber to well above that at which NO_(X) forms. Also, veryhigh mechanical compression ratios (the ratio of maximum to minimumcombustion chamber volume) are usually required to obtain compressionignition for other fuels, making the design of such engines difficult.In particular, high mechanical compression ratios mean that thecombustion chamber volume when the piston is at top dead center must bevery small, and since that volume is spread over an area at least aslarge as the piston, the thickness of the volume in the combustionchamber when the piston is at top dead center is small, which amongother things results in substantial heat transfer from the very hotgasses in the combustion chamber to the surfaces defining that volume,and further provides a large area for a given combustion chamber volumewhich can thermally quench and prevent combustion of a fuel/air mixtureimmediately adjacent that relatively large surface area.

Two fuels that have interesting possibilities for use in combustionignition engines are ammonia and natural gas. Ammonia is of interestbecause it can be manufactured from other sources of energy,particularly non-polluting sources such as wind and solar, and whenburned, merely exhausts nitrogen (assuming the temperature below whichNO_(X) will form is not exceeded) and steam which merely condenses towater vapor. Thus the products of combustion of ammonia are simplynitrogen, which already makes up approximately 80% of the atmosphere,and harmless water vapor. On the other hand, natural gas, while still ahydrocarbon, is of interest primarily because of its quantity and lowcost, which therefore has the potential of substantially reducing theU.S. dependence on foreign oil.

Fuels like ammonia and natural gas have a combination of problems.First, the high or very high mechanical compression ratios required toobtain ignition, and second, the tendency of the combustion to exceedthe temperatures at which NO_(X) is formed once ignition is obtained.Also, for a gaseous fuel, injection of the gas into a combustion chamberin sufficient quantities for immediate ignition at the temperatures andpressures adequate for self ignition is near impossible. Consequentlyfor gaseous fuels, the fuel needs to be mixed with the intake air,premixed so to speak, so control of the piston position (generallycrankshaft angle for all except free piston engine embodiments) forignition is very important, generally requiring a very versatile andcontrollable engine. Also even for liquid fuels, better mixing of thefuel and air is achievable to reduce combustion hot spots if the fueland air are similarly premixed.

In U.S. Pat. No. 3,964,452, a spark ignition engine is disclosed thatactually has a variable mechanical compression ratio. In particular,either a separate, spring loaded piston is provided in the engine headfor each combustion chamber, or the engine piston itself is springloaded so it can deflect downward when necessary. For both embodiments,once ignition is achieved and the pressure and temperature in thecombustion chamber begin to spike, the spring loaded piston deflects,actually increasing the combustion chamber volume, which limits thepressure spike and most importantly the temperature spike.

The advantages of operating a compression ignition engine as an HCCI(homogeneous charge compression ignition) engine are well known in theprior art. In accordance with such operation, fuel is pre-mixed withair, either by injection of the fuel into the combustion chamber earlyin the compression stroke, or mixed with air in the intake manifold.This allows time for vaporization of liquid fuel, and for thoroughmixing of the air and fuel, whether a liquid fuel or a gaseous fuel isbeing used. Consequently, ideally on ignition, combustion is uniformwithout the creation of hot spots, and combustion is complete because ofthe absence of fuel rich locations in the combustion chamber which donot thoroughly burn. Consequently, a compression ignition engineoperating in an HCCI mode is particularly clean and highly efficient.The difficulty, however, that is commonly encountered in the prior artis that the amount of fuel (fuel/air ratio) that may be effectively usedis quite limited, thereby limiting the power output of a particularengine to much less than the engine potentially could produce. Theproblem with adding more fuel to get more power from an engine operatingas an HCCI engine is that all of the fuel that will be injected into thecombustion chamber is already present in the combustion chamber at thetime of ignition. Thus, unless the fuel/air ratio is kept relativelylow, there will be a large spike in pressure and temperature, resultingin temperatures at which nitrous oxides are formed.

One approach for addressing this problem is disclosed in U.S. Pat. No.6,910,459 entitled “HCCI Engine with Combustion-Tailoring Chamber”. Inaccordance with that patent, for each cylinder of the engine, anauxiliary combustion chamber and an inlet passage between the maincombustion chamber and the auxiliary combustion chamber are formed inthe engine head, with a control valve controlling communication betweenthe main combustion chamber and the auxiliary chamber. Two embodimentsare actually disclosed, though both use a conventional inlet (intake)valve operating system so that the inlet valve is driven between openand closed positions in a fixed relationship with the rotation of thecrankshaft. Both embodiments also use a single auxiliary combustionchamber. The control valve, on the other hand, is electro-hydraulicallycontrolled so as to allow variable timing with respect to crankshaftrotation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an engine head arrangement of two cylinders of amulti-cylinder engine which may be used with embodiments of the presentinvention.

FIG. 2 illustrates an exemplary operating cycle of the present inventionfor a compression ignition engine in accordance with an engine of thetype shown in FIG. 1.

FIG. 3 illustrates a further exemplary operating cycle of the presentinvention for a compression ignition engine in accordance with an engineof the type shown in FIG. 1.

FIG. 4 illustrates a still further exemplary operating cycle of thepresent invention for a compression ignition engine in accordance withan engine of the type shown in FIG. 1 for providing engine braking.

FIG. 5 illustrates a further exemplary operating cycle of the presentinvention for a compression ignition engine in accordance with an engineof the type shown in FIG. 1 for recovering energy from the air in thehybrid air tank.

FIG. 6 schematically illustrates an exemplary engine head in accordancewith one embodiment of the present invention.

FIG. 7 is a schematic cross section taken along line 7-7 of FIG. 6.

FIG. 8 is a schematic cross section taken along line 8-8 of FIG. 6.

FIG. 9 illustrates three operating cycles for the present invention.

FIG. 10 illustrates 4-stroke, 8-stroke and 12-stroke cycles of operationof an alternate embodiment.

FIG. 11 illustrates further alternate cycles of operation of the presentinvention.

FIG. 12 illustrates an alternate 4-stroke cycle for the presentinvention.

FIG. 13 schematically illustrates an exemplary engine head in accordancewith one embodiment of the present invention.

FIG. 14 is a schematic cross section taken along line 14-14 of FIG. 13.

FIG. 15 schematically illustrates a further exemplary engine inaccordance with another embodiment of the present invention.

FIG. 16 illustrates an exemplary control system for the engine of FIG.15.

FIG. 17 illustrates the results, for both ammonia and gas, of a singlecylinder engine operated in accordance with the present invention withhydraulic engine valve control using a source of heated high pressureair as a substitute for a compression cylinder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present application is based on the disclosures of three separateprovisional applications. The disclosure of the first provisionalapplication is substantially repeated below.

First referring to FIG. 1, an engine head and manifolding arrangement oftwo cylinders of a multi-cylinder engine which may used with the presentinvention may be seen. Each cylinder has an intake valve I coupled tothe associated intake manifold, a pair of exhaust valves E coupled tothe associated exhaust manifold, a fourth valve A coupled to a hybridair rail, which in turn is coupled to an air tank, a fuel injector F anda pressure sensor PS. Thus in this exemplary engine, each cylinder isthe same, though that is not essential to this embodiment.

In the preferred embodiment, each cylinder may undertake differentoperations at different times, though again this too is not a limitationof the invention. The intake valve I, the exhaust valves E and the airvalve A are preferably hydraulically actuated through electroniccontrol, as is known in the art, though any control system which allowsfreedom in the timing of the operation of the valves could be used.Similarly, the fuel injector is electronically controllable in itstiming and in the amount of fuel injected in each injection event. Thefuel injector could be a gaseous fuel injector for natural gas or othergaseous fuel, or a liquid fuel injector for fuel such as ammonia.Further, fuels such as gaseous fuels and easily vaporized fuels F may beprovided to the engine through the intake manifold. Some fuels such asammonia could be used either way. Therefore using both a liquid fuelinjector for injection directly into the combustion chamber togetherwith a capability to introduce fuel into the intake manifold, the enginemay be operated on substantially any liquid or gaseous fuel, and in factmany fuels may be “injected” into either the intake system or directlyinto the combustion chamber. Also shown in FIG. 1 is a supercharger CTdriven by the exhaust to increase the pressure and temperature in theintake manifold.

Now referring to FIG. 2, an exemplary operating cycle for a compressionignition engine in accordance with an engine of the type shown in FIG.1, or more generally an engine in accordance with this embodiment of thepresent invention, may be seen. As shown therein, the horizontal axisis, in effect, the time axis, with the vertical axis being the pressurein the combustion chamber P_(C). The piston position is shown by theletters T and B, T representing the top dead center position of thepiston and B representing the bottom dead center position of the piston.It should be noted that this Figure is highly schematic in that thepressure trace is only suggestive of the pressure in a real operatingengine in accordance with the present invention. Also the engine valveoperation is not shown in FIG. 2, though will be described with respectto the following description of FIG. 2.

Now referring to FIG. 2, the exhaust valves E are closed at or near thetop dead center position T₁ and the intake valve I is opened so thatbetween the top dead center position T₁ and the bottom dead centerposition B₁, a conventional intake stroke is executed. Then at thebottom dead center position B₁ the intake valve I is closed and pistonmotion toward the top dead center position T₂ starts to compress the airin the cylinder. At a pressure which is a fraction of the maximumcylinder pressure that could be achieved, the air valve A opens todischarge the air into the hybrid air rail. The opening of the air valveA may be electronically controlled, either open loop, or by sensing theappropriate pressure by pressure sensor PS (FIG. 1) or some otherpressure sensor (not shown). Alternatively the air valve A may simply bea one-way valve which opens and closes by way of a differential pressureacross the valve. In any event, at the top dead center position T₂ theair valve A will close, after which the pressure in the combustionchamber will fall quickly because most of the air in the cylinder hasbeen already exhausted to the hybrid air rail, after which the intakevalve I will open again to carry out a second intake stroke followed bya second compression stroke.

At the top dead center position T₃ the air valve A will again close, andafter the pressure in the combustion cylinder quickly falls to or nearthe pressure in the intake manifold (which may be supercharged ifdesired), one or more of the exhaust valves E may be opened momentarilyto bring back some exhaust gas remaining from the prior operating cycle,with fuel F then being introduced (injected) into the combustionchamber. Finally, at the bottom dead center position B₃ the intake valveI is closed and the air valve A is opened for that cylinder to bring inadditional intake air from the hybrid air rail, after which the airvalve A is closed. Because the air compressed during the compressionstrokes C₁ and C₂ causes a significant rise in the air temperature, thetemperature in the combustion cylinder after introducing that air fromthe hybrid air rail will be substantially higher than is achievedthrough a normal intake stroke followed by an equivalent partialcompression stroke. Note that this is achieved before any substantialfurther compression is achieved during the compression stroke C₃ so thatmost of the mechanical compression ratio during compression stroke C₃ iseffectively maintained on the charge in the combustion chamber, thoughsuch compression starts at a substantially higher pressure andtemperature than if only a normal intake stroke had been executed.Consequently one can obtain ignition of fuels such as ammonia andnatural gas substantially at T₄, though in an engine having a mechanicalcompression ratio that is much lower than would be required to obtainsuch compression ignition, and using an amount of fuel for maximum powerthat is less than that which will cause the temperature in thecombustion chamber to rise enough to create NO_(X). In that regard, themaximum amount of fuel per combustion cycle may be approximately equalto what would be a stoichiometric amount that would be used in a veryhigh compression engine using a single compression stroke to ignition.However note that ignition has been achieved with such fuels in a muchlower mechanical compression ratio. The extra air in the lowermechanical compression ratio combustion chamber provides not only thehigher temperature needed for ignition, but also provides excess air andexhaust that does not participate in the combustion process, but whichacts as a bounce volume, so to speak, much like the mechanical provisionin U.S. Pat. No. 3,964,452. In essence, in accordance with the presentinvention, an engine of a first mechanical compression ratio may becaused to operate as if it had a second compression ratio much higherthan the first compression ratio. This eliminates the mechanicaldifficulties in achieving a mechanical compression ratio of 40 to 1 orhigher, and of also achieving a variable mechanical compression ratiolike in U.S. Pat. No. 3,964,452, but still allows achieving combustionignition in a reliable manner by simply synthesizing a high mechanicalcompression engine using a much lower mechanical compression ratioengine.

Referring again to FIG. 2, it should be noted that the introduction offuel during the intake stroke I₃ is preferred, as that is the mostconvenient part of the operating cycle of the engine for introduction offuels, particularly gaseous fuels. However in the case of a liquid fuel,such fuel could be introduced (injected) at any time prior to ignition,though in the preferred embodiment it is preferable to inject even aliquid fuel either during the intake stroke I₃ or very early in thecompression stroke C₃ to provide maximum opportunity for the fuel tovaporize and thoroughly mix with the available air. In that regard, evena gaseous fuel could be introduced later in the cycle, thoughintroduction during the intake stroke I₃ is preferred.

The foregoing description describes the cycle of FIG. 2 which is an8-stroke cycle. Obviously, more or fewer pure compression strokes may beused as appropriate to achieve the desired ignition temperature at thedesired ignition point. Also, because of the electronic control of thefuel injector and engine valves, engine valve operation may be delayedor advanced as desired to maintain the ignition point at or near the topdead center position. For this purpose, sensor PS may easily detectignition, with cycle to cycle adjustments being made in the engine valveand control system to maintain ignition at the desired point. Inessence, the degree of engine control available allows operation of theengine as a variable compression ratio engine. In that regard,preferably the engine valve control is achieved through anelectronically controlled, hydraulically operated engine valve actuationsystem for full freedom in at least valve actuation timing as desired.Examples of such hydraulic valve actuation systems are set forth laterherein.

In the foregoing description, two compression cycles are used for onefour stroke combustion cycle. Note however that this is not a limitationof the invention. By way of example, a single compression cycle may usedfor each combustion cycle such as would be effectively obtained in a sixcylinder engine by using four cylinders as combustion cylinders and twocylinders for compression cylinders. Alternatively, three (or more)compression cycles may be used for each combustion cycle. Further, thecombustion cylinder may be operated in a two stroke cycle if desired.All of these variations may be used in a single engine at differenttimes and/or for different fuels by simply applying the appropriateengine control, as it is not the engine physical characteristics thatallow any one of these operating modes, but rather it is the controlcoupled with the flexibility of the engine operation that allows thisvariation,

In general, the self ignition of a fuel/air mixture is almost entirelytemperature dependent and has very little, if any, pressure dependence.Thus a key point determining the time of ignition is the combination ofthe temperature in the combustion chamber at the beginning ofcompression of the charge, coupled with the remaining mechanicalcompression ratio that will act on that charge. As such, another way ofachieving the desired ignition temperature at the proper time would beto heat the air from the hybrid air rail so that the compression strokeC₃ begins with a hotter charge. This, too, will provide the desiredtemperature for ignition at the proper piston position if the air isintroduced at the right temperature. Accordingly, by heating the airprior to its compression during compression stroke C₃, the intake strokeI₁ and compression stroke C₁, or both sets of intake and compressionstrokes I₁, C₁ and I₂, C₂ might be dispensed with. Alternatively, one ormore compression strokes like C₁ and C₂ may be used, then the air inhybrid air rail heated and used as part or all of the air for the intakecycle. The limit, however, is that the amount of fuel injected must belimited to avoid the temperature spike that would form NO_(X) duringcombustion. Accordingly such operation may well only be suitable for lowengine loads or for idling conditions.

In comparison to trying to adapt U.S. Pat. No. 3,964,452 previouslymentioned to such alternate fuels, this embodiment does not limitcombustion chamber temperatures by limiting combustion chamber pressuresby varying the combustion chamber volume by mechanical means afterignition, but rather by simply using a larger combustion chamber tostart with. Thus the present invention is not as mechanically complex asany adaption of U.S. Pat. No. 3,964,452, and is much more suitable forincorporating into new engines without redesign of the engine block, andfor the same reason may also be suitable for retrofit of existingengines.

Now referring to FIG. 3, another exemplary operating cycle for thepresent invention may be seen. This operating cycle is a 10-stroke cyclehaving two power strokes and a single compression stroke for providingair to the hybrid air rail. Referring specifically to FIG. 3, the topdead center engine piston position T₁ is the end of a compression strokewhich may be seen at the right end of the Figure. Because most of theair that was in the combustion chamber was delivered to the hybrid airrail and the air valve A is closed, the pressure will quickly drop inthe combustion chamber as the piston moves away from the top dead centerposition T₁. When the pressure in the combustion chamber falls toapproximately the pressure in the intake manifold, the intake valves Iopen, followed by the injection of fuel by injector F and then theopening and closing of the exhaust valve E to introduce some of the hotexhaust in the exhaust manifold back into the combustion chamber. Thenapproximately at the bottom dead center position B₁ the intake valves Iclose and the air valve A opens for a short period and closes when thecombustion chamber pressure substantially reaches the pressure of theair in the hybrid air rail. Now the combustion chamber contains fuel andan exhaust gas/air mixture, which is at a substantially higher pressureand a substantially higher temperature than if a conventional intakestroke had been executed. Accordingly once the air valve A is closed,the hot intake mixture in the combustion chamber is compressed untilignition is achieved at or near top dead center position T₂. Note thatthe peak temperature obtained in the combustion chamber may becontrolled by control of the amount of fuel injected, with the exhaustgas drawn into the combustion chamber during the intake stroke providingmuch of the required initial temperature for compression prior to thepower stroke, still with the amount of air in the combustion chamberbeing more than adequate for complete combustion of the fuel.

Between the top dead center position T₂ and the bottom dead centerposition B₂ a conventional power stroke is executed, followed by theopening of the exhaust valve E for a conventional exhaust stroke betweenthe bottom dead center position B₂ and the top dead center position T₃.Then between the top dead center position T₃ and the bottom dead centerposition B₃ the same valve operation as was described with respect tothe intake stroke between the top dead center position T₁ and the bottomdead center position B₁ is executed. Similarly, between the bottom deadcenter position B₃ and the top dead center position T₄ the sameoperation occurs as occurred between the bottom dead center position B₁and the top dead center position T₂, followed by ignition and a powerstroke between the top dead center position T₄ and the bottom deadcenter position B₄. This is followed by an exhaust stroke between thebottom dead center position B₄ and the top dead center position T₅,after which the exhaust valve E is closed and the intake valves I areopened. Then at the end of the intake stroke at bottom dead centerposition B₅, the intake valves I are closed and a compression stroke isexecuted with the air valve A being opened at an appropriate time todischarge the air from the cylinder into the hybrid air rail. Then atthe end of this compression stroke the entire cycle may be repeated attime T₁.

The operation described achieves the desired temperature for ignitionthrough the combination of the use of the supercharger CT shown in FIG.1, together with the heat of compression of the compressed air beinginjected from the hybrid air rail, which can be augmented if needed byheating the pressurized air in the hybrid air rail before injection. Theexhaust gas which is taken in during the intake stroke may also heat thecharge to achieve ignition as desired without any need to heat the airbeing injected from the hybrid air rail, with that exhaust gas in thecombustion chamber merely acting to fill the combustion chamber volumewithout contributing to the combustion other than its initialtemperature so that the temperature after ignition remains below thedesired temperature, such as 2000 or 2200° K.

Now referring to FIG. 4, a diagram illustrating a possible operatingcycle for an engine decelerating, such as an engine in a vehicle inwhich engine braking is being used, may be seen. Here each intake andcompression stroke pair is used to provide air under pressure to the airtank of FIG. 1 to increase the pressure in the air tank to the pressurecapabilities of the air tank. This achieves not only increased drag bythe engine, but also stores energy in the air tank for later use.Assuming for the moment that the pressure in the air tank will thenexceed the normal pressure under operating conditions such as in thecycles of FIGS. 2 and 3, the increased pressure may be accounted for bydecreasing the time duration that the air valve is open. The stored airmay also be used in place of any compression cycles for a small periodof time so that during that time the engine may be operated in a4-stroke cycle for an increased burst of power. To the extent that evengreater engine braking is needed or desired, the engine valves may becontrolled to operate the engine in a cycle like the Jake Brake® whereinthe engine is operated in a 2-stroke cycle with the exhaust valve beingopened at top dead center so that all of the energy of compression isdissipated, ready for the following cycle intake and compression stroke.

Now referring to FIG. 5, 2-stroke cycles for operating an engine on thestored air alone may be seen. Here the hybrid air valve A is opened whenthe engine piston is at top dead center and closed at bottom deadcenter, at which point the exhaust valve is opened, and finally closedat the next top dead center position T₂. Again the air valve A is openedand a further power stroke is executed simply using the pressure of theair from the air tank to provide the pressure in the combustion chamberto operate the engine. Again the length of time an engine may beoperated this way and the power that can be achieved will depend on thesize of the air tank and the maximum pressure of the air tank. Suchoperation, however, could under various circumstances be of benefit. Byway of example, a vehicle may use the engine braking of FIG. 4 when on adown slope and the recovery of FIG. 5 in a flat region of limitedlength, which is then followed by another down slope.

The present invention allows use of fuels such as natural gas andammonia, in part because of the unique operating cycles that may beapplied to the engine and further because of the total flexibility ofthe engine in terms of operation of its various facilities undercomplete control by an electronic controller. These facilities normallywould include engine valves and fuel injectors, as previously mentioned,in terms of timing and manner of operation, but also would likely orpossibly include other operations such as perhaps the superchargerand/or supercharger baffles and the amount, if any, of the heating ofthe air from the air tank before injection, etc. It is the total controlof at least the most influential aspects of an engine which makes thepresent invention possible. Also the ability to operate the engine oneither liquid or gaseous fuels provides great versatility in the engine,and in fact for fuels such as ammonia and natural gas where ignition isdifficult, the engine might be started on one fuel such as diesel fueland then changed to another fuel such as natural gas or gaseous ammoniawhen the engine temperature allows. Also the engine might be operated onan inexpensive but low energy per unit volume fuel such as natural gas,but switched to a higher energy fuel for greater vehicle range if andwhen needed, such as diesel fuel.

One final point to consider is that this and other embodiments may becombined with a GPS input to the controller, together with a databaseeither in the vehicle in which the engine is used or at least availablefor update wirelessly. Through the use of the GPS input, together withthe elevation versus position in the database, this allows the system tolook ahead, so to speak, well beyond what is visible to the vehicledriver. By way of example, in a hilly area a driver may not know whetherthere is a substantial downgrade or upgrade around the next curve, andaccordingly, would not know whether to store as much compressed air aspossible from the last downgrade or to use that air on the present levelroad prior to encountering the next downgrade or the upgrade. Further,depending on the operator of the vehicle to make such decisions and tocontrol the air into and out of the air tank and further to control theengine operation would be a tiring diversion which an individual may notbe able to efficiently perform. Accordingly, a GPS input of currentposition, together with a database of altitude versus position, canallow the main control system for the engine to make such decisions in amost efficient and prompt manner.

The disclosure of the second provisional application is substantiallyrepeated below.

This embodiment uses flexible intake and exhaust valves (such ashydraulically actuated engine valves with electronic control) to achieveHCCI combustion over 100% of the load with any fuel. This approach isapplicable to new and existing engines for any application. The basicapproach is to adjust the geometrical compression ratio (typically bycontrol of the intake valves) to a minimum level that is stillsufficient to ignite a full charge (air and fuel mixture) sufficient toachieve a full load. This will provide sufficient volume at the end ofthe compression stroke to avoid an explosion while providing optimumcombustion. For example, for natural gas, ignition will occur at 1072°K. By keeping the peak temperature below 2200° K, no NO_(X) emissionswill be formed.

When less than full load is required, the ideal air/fuel ratio will bepre-mixed and compressed. There are several methods available to achievethe ignition temperature (for the given example of natural gas 1072° K):

1) Disabling a certain number of cylinders so that remaining cylindersremain operating at full load.

2) Opening the exhaust valves during the intake stroke in such a waythat the mixture of air, fuel and exhaust will reach the ignitiontemperature at the desired position.

3) Controlling the intake valve timing.

Ideally the process could be controlled in a closed loop system byproviding a pressure sensor in each cylinder and a microprocessor withproper software to fully optimize the operation of the system under anycondition.

The disclosure of the third provisional application is substantiallyrepeated below.

Now referring to FIG. 6, an exemplary engine head in accordance with oneembodiment of the present invention is schematically shown. Eachcylinder includes a conventional intake valve 20, a conventional exhaustvalve 22, and additional air valves 24 and 26. Also shown are a fuelinjector 28 and a pressure sensor 30. A turbocharger comprising anexhaust driven turbine 34 connected to the exhaust manifold 32 drivingcompressor 36 provides an elevated pressure in the intake manifold 64.In that regard, fuel such as a gaseous fuel may be mixed with air in theintake manifold 64 as is well known in the art or in the cylinder duringthe intake stroke, or alternatively or in addition, a liquid fuel may beinjected directly into the combustion chamber 38 (FIG. 7), though asshall be subsequently explained in detail, any such injection of aliquid fuel would occur early in the compression stroke or even duringthe intake stroke to provide both full vaporization of the liquid fuelbecause of the temperatures in the combustion chamber 38, particularlybecause of the compression to take place therein, and also to fully mixwith the air in the combustion chamber 38.

Now referring to FIG. 7, a schematic cross section taken along line 7-7of FIG. 6 may be seen. This is a schematic cross section taken throughthe intake valve 20, the fuel injector 28 and the exhaust valve 22. Asmay be seen therein, this schematic cross section is in generalrepresentative of such a cross section in substantially any overheadvalve compression ignition engine currently in use.

FIG. 8 is a schematic cross section taken along line 8-8 of FIG. 6. ThisFigure schematically shows the cross section through the air valve 24,the fuel injector 28 and the air valve 26. Air valve 24 controls thecoupling between the main combustion chamber 38 above piston 40 and afirst secondary volume 42. Air valve 26, on the other hand, controls thecoupling between the main combustion chamber 38 above the piston 40 anda second secondary volume 44. Both of these volumes as well as volume 44in FIG. 14 are dead volumes in the sense that they do not lead anywhere,as opposed to a conventional engine valve that normally leads to amanifold. In a preferred embodiment, the volume of the second secondaryvolume 44 is less than the volume of the first secondary volume 42,though that is not a limitation of the invention. As may be seen in theFigure, air valves 24 and 26, like the intake and exhaust valves 20 and22 of FIG. 7, are controlled by hydraulic actuator/valve springassemblies 46, which in turn are controlled by control valves 48 on topof the actuator 46. Similarly, the injector 28 is controlled by aninjector control valve 50 on the top thereof, with the control valves 48and 50 being electromagnetically actuated control valves which also maybe actuated at any time, independent of the crankshaft position.

The liquid fuel injectors of this and the other embodiments may beintensifier type fuel injectors electronically controlled through spoolvalves of the general type disclosed in one or more of U.S. Pat. Nos.5,460,329, 5,720,261, 5,829,396, 5,954,030, 6,012,644, 6,085,991,6,161,770, 6,257,499, 7,032,574, 7,108,200, 7,182,068, 7,412,969,7,568,632, 7,568,633, 7,694,891, 7,717,359, 8,196,844, 8,282,020,8,342,153 and 8,366,018, and U.S. Patent Application Publication Nos.2002/0017573, 2006/0192028, 2007/0007362, 2010/0012745, 2010/0186716 and2011/0163177. These patents and patent applications discloseelectronically controllable intensifier type fuel injectors havingvarious configurations, and include direct needle control, variableintensification ratio, intensified fuel storage and various otherfeatures.

The electronically controllable valve actuation system of this and allthe other embodiments may be a hydraulic valve actuation systemcontrolled by spool valves of the general type disclosed in one or moreof U.S. Pat. Nos. 5,638,781, 5,713,316, 5,960,753, 5,970,956, 6,148,778,6,173,685, 6,308,690, 6,360,728, 6,415,749, 6,557,506, 6,575,126,6,739,293, 7,025,326, 7,032,574, 7,182,068, 7,341,028, 7,387,095,7,568,633 7,730,858 and 8,342,153, and U.S. Patent ApplicationPublication Nos. 2007/0113906 and 2010/0277265. These patents and patentapplications disclose hydraulic valve actuation systems primarilyintended for engine valves such as but not limited to intake and exhaustvalves, and include, among other things, methods and apparatus forcontrol of engine valve acceleration and deceleration at the limits ofengine valve travel as well as variable valve lift.

Now referring to FIG. 9, three operating cycles for the presentinvention may be seen. The first operating cycle illustrated is a4-stroke operating cycle. In FIG. 9, the four strokes are labeledintake, compression (Compr.), power, and exhaust, and schematicallyillustrate the pressure in the combustion chamber 38 as the piston 40moves from the top dead center position (T) to the bottom dead centerposition (B), and vice versa, with the numerals following T and Bindicating the number of that type of stroke for the cycle beingdescribed. Starting at the beginning of the intake stroke (top deadcenter position T1), the air valve 26 (A₂O.) and intake valve 20 areopen (I.O.), and during the intake stroke, if a gaseous fuel is beingused, a fuel/air mixture is drawn or forced into the combustion chamber38 by the compressor 36. If a liquid fuel is being used, then merely airis drawn or forced into the combustion chamber 38. At the bottom deadcenter position B1, the intake valve 20 is closed (I.C.), andalternatively, if a liquid fuel is being used, the fuel is preferablyinjected shortly after the intake valve 20 is closed (in some cases botha liquid and a gaseous fuel might be used). During this time the airvalve 26 is open and remains open during a substantial portion of thecompression stroke.

At some point in the compression cycle, air valve 26 is closed (A₂C.),with ignition (Ign) occurring at or near the top dead center positionT2. The pressure sensor 30 senses the increasing pressure in thecombustion chamber, and before the pressure and temperature can peak,air valve 26 is opened (A₂O.). The opening of air valve 26 afterignition couples volume 44 to the then existing volume of combustionchamber 38 so that the pressure and temperature spike is limited becauseof that increase in volume and the lower pressure in that volume. Inthat regard, the volume 44 will already be at a substantial pressurebecause of the air valve 26 being closed well into the compressioncycle, and in addition will contain some fuel/air mixture which will beconsumed when air valve 26 opens and the mixture is ignited from thecombustion occurring in the main combustion chamber 38. Still, theopening of air valve 26 after ignition occurs will limit the pressureand temperature spike obtained for various reasons, including the factthat the pressure in volume 44 when air valve 26 is closed will besubstantially less than when the air valve 26 is opened again near thetop dead center position T2.

During the power stroke, the piston 40 will move between the top deadcenter position T2 and the bottom dead center position B2, with theexhaust valve 22 being opened (E.O.) at or near the bottom dead centerposition B2, after which the exhaust valve 22 is opened and aconventional exhaust stroke is executed between the bottom dead centerposition B2 and the top dead center position T3, which is effectivelythe top dead center position T1 of the next cycle.

Also illustrated in FIG. 9 are 8-stroke and 12-stroke cycles. These arein essence the 4-stroke cycle followed by four or eight dead or inactivestrokes. In the embodiment shown in FIG. 9, after the exhaust strokebetween the bottom dead center position B2 and the top dead centerposition T3, the exhaust valve 22 is left open and the intake valve 20is also opened throughout these additional strokes so that nosignificant pressure or pressure fluctuations exist in the combustionchamber 38 until at the top dead center positions T5 and T7 for the8-stroke and 12-stroke cycles, respectively, at which T5 and T7positions become the T1 positions for a repeat of the 8-stroke and12-stroke cycles. Of course, during these additional strokes no fuel isinjected into the combustion chamber 38 by the fuel injector 28 nor isany fuel injected into the intake manifold 64 if a gaseous fuel is beingused.

Referring to FIG. 10, 4-stroke, 8-stroke and 12-stroke cycles of analternate embodiment may be seen. The 4-stroke cycle may be the same asthe 4-stroke cycle of FIG. 9. However for the inactive cycles theexhaust valve 22 is closed at the end of the exhaust cycle (top deadcenter position T3) and remains closed until the end of the next powerstroke. As such, the pressure in the combustion chamber 38 at the topdead center position T3 when the exhaust valve 22 is closed will be onlyslightly above atmospheric pressure, with the further strokes firstdecreasing that pressure then increasing the pressure back toapproximately atmospheric pressure and repeating such strokes until thelast top dead center position (T5 or T7) which corresponds to the firsttop dead center position T1 of the next cycle. Obviously if desired,6-stroke and 10-stroke operation or operation with any other even numberof strokes may be used, as desired.

The advantage of using air valve 26 to couple and decouple volume 44from the combustion chamber 38 is that it allows a sudden increase inthe combustion chamber volume and decrease in the combustion chamberpressure, and thus a decrease in the combustion chamber pressure andtemperature spike, to allow operation of the engine at a maximum powersetting, i.e., allowing fuel/air ratios to approach the stoichiometricfuel/air ratios without NO_(X) generation. For operation under otherpower settings, one would need to evaluate the overall engine efficiencyunder various power settings to determine at each power setting whetheroperating on a 4-stroke cycle using the equivalent of a very leanfuel/air ratio would be most efficient or whether using a higherfuel/air ratio with a 6, 8, 10 or 12-stroke cycle would be moreefficient.

Now referring to FIG. 11, further alternate cycles may be seen. The4-stroke cycle shown in FIG. 11 is also identical to the 4-stroke cycleof FIGS. 9 and 10. In the 8-stroke and 12-stroke cycles, however, afterthe power stroke at the bottom dead center position B2, the exhaustvalve 22 is not opened, and accordingly additional compression andexpansion strokes occur until after the last expansion stroke (B4 forthe 8-stroke cycle and B6 for the 12-stroke cycle). The exhaust valve 22is then opened (E.O.) and a normal exhaust stroke is executed, afterwhich the exhaust valve 22 is closed (E.C.) for repeat of the entirecycle. As a still further alternate, the exhaust valve 22 could beopened at the bottom dead center position B2, after which the intakevalve 20 could be opened at the top dead center T3 to take in coolerair, with the intake valve 20 being closed at the bottom dead centerposition B3, after which one or more compression and expansion strokeswould occur before doing a final exhaust stroke (between B4 and T5 orbetween B6 and T7), with the cycle then repeating. Alternatively, thecycle need not repeat until the bottom dead center position B1 isreached, i.e., a second intake stroke is not used.

In all of these extra cycles, there will be some losses which willdiffer depending on which form of extra cycles is used. These losses areprimarily friction losses, heat losses and flow losses. Friction lossesprobably do not vary that much with the differing extra cycles, thoughheat losses depend on the difference in temperature between the contentsof the combustion chamber 38 and the walls of the combustion chamber.Accordingly, the extra cycles of FIGS. 9 and 10 are probably moreefficient than the extra cycles of FIG. 11, though all should beevaluated, both for efficiency and convenience. By way of example, theextra cycles of FIG. 9, wherein the intake valve 20 and exhaust valve 22are both left open during the extra cycles, may result in excessive flowlosses and generate undesirable noise levels.

In the foregoing description, no particular function of volume 42 or ofthe operation of air valve 24 has been disclosed. This air valve 24,when open, increases the volume of the combustion chamber 38 and isintended to either be left open, having the effect of decreasing theinherent compression ratio, or being left closed, in effect increasingthe compression ratio of that cylinder. Thus the compression ratio withair valve 24 closed can be made quite high, though reduced by operatingthe engine with air valve 24 open for fuels which are more easilycompression ignited. Of course, in any event, one would control thevalves, particularly the intake valve 20 with respect to the timing ofits operation, to control the position of piston 40 when ignitionoccurs, with cycle to cycle corrections being made as required tomaintain the ignition point at the desired piston position, ignitionbeing sensed by pressure sensor 30. In that regard, the time of closingthe air valve 24 will also have an effect on when ignition occurs,though it is preferable to dedicate the function of the air valve 24 tolimiting the temperature spike and use the timing of the intake valve 20to control the time of ignition.

Further, of course, one may not want to open the air valve 26immediately when ignition occurs, as it is possible that doing so maydrop the temperature in the combustion chamber so that combustion doesnot continue. Consequently it may be desirable to impose a short delaybefore opening the valve 26 to avoid such an occurrence.

Thus in the embodiments disclosed so far, air valve 24 in essencecontrols the static compression ratio of that cylinder of the engine,whereas air valve 26 controls (limits) the pressure and temperaturespike that is obtained after ignition of a full fuel charge during highenergy output by dynamically varying the compression ratio. Obviouslyeither air valve 24 or 26 could be used for either purpose, and ofcourse for some lower power settings of the engine, air valves 24 and 26may both be left in fixed positions (open or closed) when the fuel/airratio is too low to create pressure and temperature spikes that willgenerate NO_(X). In addition, if volumes 42 and 44 are equal, one canalternate the functions of the air valves 24 and 26 and respectivevolumes 42 and 44 to help prevent excessive temperatures of the airvalves 24 and 26. Alternatively, the volumes 42 and 44 may be purposelymade unequal, which provides greater flexibility in the ability tocontrol compression ratios of that cylinder, as either air valve 24 or26 or both may be used for static or dynamic compression ratio control.This together with the electro-hydraulic control of the air valves 24and 26 as well as the intake valve 20 and exhaust valve 22 provides ahigh degree of flexibility in the operation of an engine to ensure themost efficient operation and a maximum possible peak power outputwithout generating NO_(X). Both static and dynamic compression ratiosare controllable, the time of compression ignition is controllable,primarily by control of the time of the closing of the intake valve 20,and the degree of suppression of the pressure and temperature spike isalso controllable as required by the power setting, primarily bychoosing the volume 42 and/or 44 of the auxiliary combustion chambersand by controlling the time of closure of the respective air valve(s) 24and 26 to control the pressure difference between the volume ofcombustion chamber 38 and the respective auxiliary combustion chambervolumes 42 and/or 44.

One other aspect of the present invention is its flexibility inincorporation in both new and existing engines. In particular,substantially all engines currently on the road use two intake valvesand two exhaust valves per cylinder, thereby providing the four valvesneeded with the present invention. Further, as shown in FIG. 8, theauxiliary combustion chamber volumes 42 and 44 are preferably defined byinserts 54 and 56, which may be incorporated into existing head designswith minor modification, either in the head design for new engines or byway of reworking or modifying the heads in preexisting engines. In thatregard, the valve actuation system can be easily provided as a bolt-onsystem to existing heads or head designs so that any rocker armassembly, push rods, etc. may be removed from the engine. The camshaftitself may be left in existing engines, if desired, as the existing heador heads may be swapped out for already reworked heads or themselvesreworked or modified in accordance with the present invention withouttaking the engine out of the vehicle as may be required for removal ofthe engine camshaft. Removal of the camshaft is not necessary as therotation of the camshaft without any load thereon takes a negligibleamount of power. Thus the present invention may be operated in what iscommonly referred to as an HCCI (homogeneous charge compressionignition) mode, known for its lack of carbon emissions, and controlledin accordance with the present invention at high power outputs asrequired to prevent any formation of NO_(X).

In the disclosure above and in the claims to follow, references are madeto top dead center positions and bottom dead center positions, which ofcourse refer to the piston positions in the respective cylinder. Howeverit is to be understood that these piston positions when being used toreference valve operation or ignition in the disclosure and the claimsto follow are approximate only, and are to be interpreted as meaning ator near the respective piston position, irrespective of whetherindicated as being at or near.

FIG. 12 represents an alternate approach which decouples the control ofthe start of ignition from the start of the spike suppression function.The timing of the closing of air valve 24 (A₁C) controls the start ofignition and the opening of air valve 26 (A₂O) or both air valve 24(A₁C) and air valve 26 (A₂O) controls the start of the suppressionevent. Note that the timing of the opening of air valve 26 (A₂O) is notidentified in FIG. 12, as the same may be closed at any time from nearthe end of the power stroke to trap some exhaust gas to preferablybefore the beginning of the compression stroke. Note also, that the airchambers of FIG. 8 are of different size, though this is not alimitation of the invention. If they are of different sizes, which willbe for ignition timing and which for spike suppression may depend on thecharacteristics of the fuel being used, mainly the ease with which itcompression ignites and the energy content of the fuel. This approachgreatly improves the dynamic control of the combustion process. This4-stroke cycle may be used in any of the embodiments described withrespect FIGS. 9, 10 and 11, and like those embodiments, are merelyexemplary of the flexibility provided by two controllable volumes in acamless engine design. Such combustion cylinder volume control can beused with other embodiments also if incorporated into such engines.

Now referring to FIG. 13, an engine head in accordance with an alternateembodiment may be seen. This embodiment includes intake valves 20,exhaust valves 22, air valves 24 and 26, fuel injectors 28, and pressuresensors 30, as well as intake manifold 64, exhaust manifold 32, exhaustdriven turbine 34 and compressor 36 of FIG. 6. In addition, however, anair rail 52 coupled to air tank 61 is added. Also in this embodiment,each air valve 24 is coupled to the air rail 52 through a respectiveauxiliary valve 58.

A cross section of this head through the air valves 24 and 26 as shownin FIG. 8 is identical with respect to the injector 28, injector controlvalve 50 and everything to the right of the injector 28 of FIG. 14.Similarly, the air valve 24, hydraulic actuator 46 and control valve 48may be the same as that shown in FIG. 7. However, insert 54 need not beused, as the volume 42′ together with the porting 60 (FIGS. 13 and 14)serve the same purpose. Of course, alternatively, such an insert 54 maybe used or the equivalent of volumes 42 and 44 (FIG. 8) designed intonew heads for existing engines. However in the case of retrofittingexisting engines by reworking their existing heads, reworking the headsto include inserts 54 probably would not justify the cost of doing so,though in some cases, it may be necessary to actually decrease thepreexisting available volume by some insert of some kind.

The embodiment of FIGS. 13 and 14 may be operated in various modes. Byway of example, with the air valves 58 closed (FIG. 13), all cylindersmay be operated in the same manner as hereinbefore described withrespect to the embodiment of FIGS. 6-8. In a second mode of operation,used for both braking and energy storage, fuel may be shut off and airvalve 26 and exhaust valve 22 left in the closed position, but with theintake valve 20 operated in the normal manner. Then at the end of acompression stroke, air valve 24 would be opened, delivering highpressure air to the air tank 61 for later use. (Alternatively theexhaust valve 22 could be opened to vent the high pressure in thecombustion chamber 38 to the atmosphere.) On filling of the air tank,additional high pressure air may be vented to atmosphere through apressure relief valve 62, or by opening the exhaust valve 22 at the topdead center position of the piston 40 as described above. Such operationis essentially a 2-stroke cycle operation, in that startingapproximately at top dead center position of the piston 40 the intakevalve 20 may be opened and an intake stroke bringing air into thecombustion chamber is executed. Then when the following compressionstroke causes the pressure in the combustion chamber 38 to somewhatexceed the pressure in the air tank, air valve 24 is opened to deliverthe high pressure air to the air rail 52, and then closed at the topdead center position so that the intake valve 20 may be opened after thetop dead center position to carry out another intake stroke for thefollowing cycle.

Another mode of operation is to inject air into the combustion chamber38 through air valves 24 and 58 from the air tank 61 at some pointduring the compression stroke. This can be used to increase the totalamount of air in the combustion chamber 38, allowing the injection of agreater amount of liquid fuel through each injector 28, and for a longerperiod, so that the combustion occurs over a wider crankshaft angle toprovide substantially increased power output of the engine. Obviouslythis will be limited by the size of the air tank, though can be quitebeneficial for bursts of power when needed.

Another mode of operation is to operate one or more cylinders ascompression cylinders using the intake valve 20 for the intake strokeand then opening air valve 24 and air valve 58 near the end of thecompression stroke, if air valve 58 is not already open, to deliver highpressure air to the air tank, closing air valve 24 before the subsequentintake stroke begins. In this mode of operation, air valve 26 andexhaust valve 22 in the compression cylinders are not used. Othercylinders would be used as combustion cylinders with the high pressureair in the air tank 61 being injected into the respective combustioncylinders through air valves 24 and 58 reasonably late in thecompression stroke and/or during the power stroke to allow longerinjections of fuel and, again, maintain combustion and therefore highcombustion chamber pressures over a wider range of crankshaft angle formore favorable energy conversion. Note that because all cylinders arethe same, any one cylinder may be periodically alternated between use asa compression cylinder and use as a combustion cylinder to betterdistribute wear and engine heating for better functioning of the(preexisting) engine cooling system.

The foregoing modes of operation are exemplary only, and many othermodes of operation are possible, including those of FIGS. 9-11 and anyof the modes or adaptations of the modes disclosed in U.S. Pat. Nos.6,415,749, 7,954,472, 7,958,864 and 7,793,638, and U.S. PatentApplication Publication No. 2008/0264393.

Now referring to FIG. 15, a further embodiment of the present inventionmay be seen. Shown therein is a schematic diagram of a six cylinderengine with the left three cylinders being used as compression cylindersand the right three cylinders being used as combustion cylinders. Asshown therein, a compressor or supercharger 66 is driven by the exhaustturbine 68 to deliver air to the intake manifold 70 at a temperature andpressure that are higher than atmospheric. Each of the cylinders, bothcompression and combustion cylinders, have four poppet valves, a fuelinjector F and a pressure sensor S. For the compression cylinders, threeof the poppet valves I are coupled to the intake manifold and used foringesting air into the compression cylinders from the intake manifold 70for compression therein. The fourth poppet valve A in each of thecompression cylinders delivers air at a substantially further elevatedpressure and temperature to the air rail 72, with an optional air tank74 providing both a high pressure air storage capability and reducingpressure fluctuations in the air rail.

The pressure sensor S in the compression cylinders can be used to sensewhen the poppet valves A should be opened so that the desired pressureis maintained in the air rail. Alternatively, the valves A could besimple check valves which open when the pressure in a respectivecompression cylinder exceeds the pressure in the air rail 72 andotherwise remain closed. Except for the possible use of such a checkvalve, the poppet valve operation is preferably electronicallycontrollable, such as by way of example, using a hydraulic valveactuation system such as that disclosed in the patents hereinbeforereferred to. Thus the engine will be a camless engine with total freedomin the timing of actuation of the poppet valve, and further may alsohave an electronically controllable valve lift, if desired.

The fuel injectors F_(G) shown in the compression cylinders areinjectors for gaseous fuel such as compressed natural gas (CNG) andammonia (NH₃), though other gaseous fuels could be used if desired. Thegaseous fuel is injected into the compression cylinders during or beforethe compression stroke, and in fact could be injected during the intakestroke of the compression cylinder to assure the maximum possible mixingof the gaseous fuel and the air in or going into the compressioncylinder. Thus if a gaseous fuel is being used, the air rail 72 willcontain a gaseous fuel/air mixture less than or near the stoichiometricfuel/air mixture that is very well mixed prior to being passed to thecombustion chambers.

The combustions chambers each include a poppet valve A for the intake ofpressurized air or pressurized air/gaseous fuel mixture from the airrail 72 and two exhaust valves E for exhausting combustion products tothe exhaust manifold 76. A fourth valve B may be in accordance with airvalve 2 in FIG. 14, having a chamber such as bell shaped chamber 44thereabove to provide the capability of a step change in the mechanicalcompression ratio of the combustion cylinders to limit the pressure andtemperature spike that would otherwise be obtained for a nearstoichiometric fuel/air ratio when operating with the HCCI combustioncycle.

Also, each combustion cylinder includes a liquid fuel injector F_(L) forinjection of a liquid fuel, such as by way of example, diesel fuel orbiodiesel fuel, though other liquid fuels might also be used, includingliquid fuels such as gasoline or substantially any other liquid fuelthat releases enough energy on combustion to be useful in an engine.Such liquid fuels might also include, by way of example, ammonia (NH₃),dependent on whether the ammonia fuel normally stored in the liquidstate under substantial pressure would be maintained in the liquid format the temperatures required, as opposed to being reduced in pressure toturn into a gaseous state for injection in the compression cylinders asjust described. Of course, as a further alternative, gaseous ammonia orany other gaseous fuel could be mixed with air in the intake manifold 70without the use of a fuel injector F_(G) in the compression cylinders.In that regard, even some liquid fuels such a gasoline could be mixedwith air in the intake manifold 70 if desired.

In operation, using a liquid fuel such as diesel fuel, the valves in thecompression cylinders may be operated so that on the intake stroke of agiven cylinder the intake valves I are open. The intake valves I arethen closed at the bottom of the intake stroke and the air in therespective cylinder is compressed during the compression stroke, withthe valve A being opened when the pressure in the respective compressioncylinder is equal to or slightly above the pressure in the air rail 72.Since the compression cylinders in the exemplary method of operationbeing described operate on a 2-stroke cycle, whereas the combustioncylinders operate on a 4-stroke cycle, there will be two compressioncycles for each combustion cycle in each respective combustion cylinder.

For the combustion cycle, the exhaust valves E will be opened at the endof a combustion or power stroke, with the contents of the combustioncylinder being emptied into the exhaust manifold during the followingexhaust stroke. Then at the top of the exhaust stroke, the exhaustvalves E are closed and the air valve A is opened to pressurize thecombustion cylinder to the pressure in the air rail 72 and air tank 74,if used. Then during the following stroke the cylinder is filled withair at the pressure of the air rail, which of course is substantiallyabove atmospheric pressure. Accordingly, some power is recovered fromthe elevated air pressure in the combustion cylinder, though at thebottom dead center position the amount of air in the combustion cylinderwill be approximately twice what would have been there with aconventional intake stroke, as each compression cylinder has undergonetwo compression strokes for each combustion cycle in the combustioncylinders. Of course associated with that higher pressure in thecombustion cylinder is the higher temperature of the air thereinresulting from its net compression in the compression cylinders.Preferably during that intake stroke of air from the air rail 72 throughvalve A, the liquid fuel is injected through the fuel injector F_(L) inan amount dependent upon the power output demand of the engine. Thisassures excellent mixing of the liquid fuel with the air in thecombustion chamber, in part because of the turbulence of the rush of airinto the combustion cylinder and in part because of the elevatedtemperature in the combustion chamber converting the liquid fuel to agaseous state, at least for most liquid fuels.

Then on the following compression stroke the charge in the combustionchamber, already at an elevated pressure and temperature, is furthercompressed by the compression stroke to achieve compression ignition ator near the top dead center position, followed by the combustion orpower stroke, after which the exhaust valves E are opened to repeat thecycle.

For higher power settings where the fuel/air ratio is closer to thestoichiometric ratio, combustion chamber temperatures in the combustioncylinders would reach temperatures at which NO_(X) is formed.Accordingly, for these power settings the valve B may be opened justafter compression ignition occurs to provide an increase in thecombustion chamber volume to reduce the pressure and temperature risetherein to maintain the combustion temperatures to a temperature belowwhich NO_(X) is formed. Thus the operation of the valve B is generallyin accordance with the operation of the pilot valve 26 of FIG. 8 ashereinbefore described.

With respect to operation using a gaseous fuel, the fuel injectors S_(L)in the combustion cylinders are not used, but rather the fuel/air ratioalready provided in the air rail from the compression cylinders will bepassed into the combustion cylinders through valve A for compressionignition on the next compression stroke. Otherwise, operation using agaseous fuel will be as described with respect to the use of a liquidfuel, with the valve B being used if and when required to prevent theformation of NO_(X).

When using a gaseous fuel, one might choose to not use the optional airtank 74, even if present, and close valve 78 for two reasons. First, thefuel/air ratio in air rail 72 would not be immediately controllablebecause of the fuel/air ratio in the contents of air tank 74. Also, iffor some extraordinary reason a fuel/air mixture in the air tank 74 wasignited, the pressure capabilities of the air tank might be exceeded,with highly undesirable consequences. In that regard, the air rail,being of relatively small internal diameter and typically of arelatively thick wall, would itself probably not be harmed by such abackfiring. However, particularly when operating the engine on a liquidfuel, the air tank 74 may be used not only to smooth out pressurefluctuations in the air rail 72, but may also be used for energystorage, such as during use of the engine for braking purposes. Suchstored energy could be used later to provide a burst of power whenoperating on a liquid fuel by substantially increasing the pressure inthe combustion chamber prior to ignition, which of course would increasethe total output power of the engine while that air at the extrapressure is being used. If the storage capability is high, the enginemight actually be run on high pressure air for a short time.Alternatively the stored energy in the compressed air in the storagetank may be used to supply air at an elevated pressure to the air rail,thereby reducing the amount of air that the compression cylinders needto compress, thereby reducing the energy used by the compressioncylinders

As before, as may be seen from FIG. 15 and the description of operationof the engine schematically illustrated therein, the effectivecompression ratio in the combustion cylinders substantially exceed themechanical compression ratio of the combustion cylinders, and in fact,can have an effective compression ratio approaching twice the mechanicalcompression ratio of the combustion cylinders, assuming the compressionand combustion pistons diameters and strokes are equal. This allows theattainment of the high compression ratios and temperature required forcompression ignition of a fuel like ammonia without mechanicallyrequiring such a compression ratio in a single cylinder. Consequently,such an engine as schematically shown in FIG. 15 operates in an HCCIcycle because of the early injection of the fuel, not only of a gaseousfuel but of a liquid fuel also, when used by injecting that fuel not atthe end of the respective compression stroke as in conventionalcompression ignition engines, but rather preferably early in thecompression stroke, and even more preferably during the intake of airfrom the air rail 72, which provides maximum opportunity for uniformmixing and conversion of the liquid fuel to a gaseous form beforeignition.

In the foregoing description of the engine of FIG. 15, compressionignition at or near the top dead center piston position at the end ofthe compression stroke in a combustion cylinder was assumed withoutdiscussing how the same is obtained. In particular, since the fuel andair are essentially thoroughly premixed to form a homogeneous charge,the fuel/air mixture will go through compression ignition duringcompression when the temperature in the combustion chamber reaches theignition temperature which, without control, may happen too early in thecompression stroke or, alternatively, not happen at all. Accordingly,careful control of the compression ignition timing is essential toproper engine operation. This is facilitated in part by the electroniccontrol of the compression cylinder valves and the combustion cylindervalves and in part by the manner in which they are controlled. Inparticular, an exemplary control system for the engine of FIG. 15 may beseen in FIG. 16. As shown therein, the controller is responsive to apower setting, such as by way of an accelerator in a vehicle, to an airrail temperature, and to the pressure sensors in the various cylindersto control the twelve compression cylinder valves, the twelve combustioncylinder valves, the three gas fuel injectors, the three liquid fuelinjectors, the air tank valve and the supercharger based on theseinputs. In an engine of the type being described, which will operate onboth liquid and gaseous fuels, other inputs might include an input ofthe fuel type or types available and the fuel type selection. Inparticular, a vehicle may have two or more fuel tanks carrying differentfuels, with the controller being provided with knowledge of what thosetwo different fuels are and what fuel type has been selected for currentoperation of the engine. If two fuel types are available, the two typesmight be one liquid fuel and one gaseous fuel, though could be twodifferent types of liquid fuels or two different types of gaseous fuels.The two different fuels might be, by way of example, a high energycontent fuel and a low energy content fuel, with the engine switchingback and forth between fuels dependent on the power setting. In thatregard, because the controller would know the various valve operationsrequired to obtain ignition at the desired time, such as by way ofvarious lookup tables and sensed information such as the air railtemperature, switching back and forth between two different fuels,whether done regularly or infrequently, is a unique capability of theengines of the present invention.

The fuel types available might also be a low cost fuel capable ofproviding a limited vehicle range because of its limited storage energydensity, such as by way of example, compressed natural gas, togetherwith a second fuel that can be stored in liquid form for use when thevehicle range needs to be extended. Such a fuel might be conventionaldiesel fuel as a liquid fuel or a gaseous fuel which may be stored inliquid form, such as ammonia. Further, the two fuels might be selectedbased on other considerations such as based on availability at variousdestinations of the vehicle. The two fuels might also be selected basedon their starting ease, such as the combination of a diesel fuel(perhaps even thinned with a percentage of gasoline) and ammonia. Insuch a combination the engine could be started on the diesel fuel usinga conventional 4-stroke diesel cycle (injecting the diesel fuel into thecombustion chamber at or near the top dead center position of thecompression stroke) and then switching to HCCI operation when the enginewarms up enough for that operation, and eventually to operation on theammonia when allowed by the engine operating conditions.

In the control of the engine, the maximum effective compression ratio isobtained by using two full compression strokes in the compressioncylinders for each combustion cycle in the combustion cylinders. Using acompression ratio in an individual cylinder of 20-25:1, the effectiveoverall compression ratio is on the order of 40-50:1, more than enoughto ignite even difficult to ignite fuels. The compression ratio may bereduced from that maximum by closing the intake valves I of thecompression cylinders before a full compression chamber charge of airhas been obtained. This, then, limits the amount of air beingcompressed, which in turn limits the pressure in air tank 74, if used,and further limits the initial compression of the air introduced intothe combustion cylinders through the valve A. Thus the maximum pressureand temperatures achieved in the combustion cylinders on the compressionstroke will be reduced from the maximum just described, which reductionmay be reduced almost without limit to an average air rail pressure ofeven less than atmospheric, so that the effective compression ratioachieved in the combustion cylinders is actually less than themechanical compression ratio of those cylinders. This controllability,together with the pressure sensors particularly in the combustioncylinders, allows sensing the timing of the initiation of combustion toallow the adjustment of the next combustion cycle. In that regard, whilethe amount of air being compressed in the compression cylinders may befairly quickly reduced or increased, the pressure in the air rail 72 maylag, particularly if valve 78 is open so that air tank 74 is active.However for fine adjustment, the amount of air allowed into thecombustion cylinders may itself be controlled by closing the valve A ofthe combustion cylinders slightly before the end of the intake strokefor the combustion cylinders to allow adjustment of that closing time,which in turn will provide an adjustment on the maximum compressiontemperature in the combustion cylinders for ignition (as compressionignition is temperature dependent, not pressure dependent). Thus shortterm adjustments may readily be made by control of the valves in thecombustion cylinders to maintain compression ignition at the desiredtime, with longer term adjustments being made by control of the amountof air being compressed in the compression cylinders.

As a confirmation of the inventions set forth herein, and theexceptional controllability of such engines by the electronic control ofthe fuel and engine valve operation, a single cylinder engine with thehydraulic engine valve control was operated using a source of heatedhigh pressure air as a substitute for a compression cylinder. Theresults are shown in FIG. 17 for both ammonia and natural gas. The plotsshown therein are 100 cycle overlays of the pressure profiles for thetwo different fuels in bar. Note that the pressure for compressionignition of ammonia was approximately 125 bar while the pressure forcompression ignition of natural gas was approximately 80 bar. Therepeatability of the pressure profiles is outstanding.

It was previously mentioned that in an engine system that has energystorage capabilities, such as an internal combustion engine withcompressed air storage, a GPS system with a database of informationregarding hills in roadways could be used to manage the operation of theenergy storage system to maximize system efficiency and power when it isneeded by determining when stored energy should be used or conserved asmuch as possible. By way of example, using the three dimensional sensingcapabilities of GPS, if a downgrade is coming, the stored energy couldbe used before reaching the downgrade, and replenished when using theengine for braking on the downgrade. On the other hand if an upgrade iscoming, the opposite may be the case. Either of these possibilities maybe just around a curve, or even if visible, this is not something adriver can manage with accuracy and without tiring quickly. With adatabase of such information, however, the same may be automated, withthe power setting set by the vehicle operator automatically beingadjusted for the power required for energy storage and/or the poweradded from the stored energy, as the case may be.

If or until information on highway elevation versus position isavailable at a reasonable cost, one could simply use general elevationversus position as an approximation of the actual highway elevationversus position, if available. As a further alternative, one could use aself learning system by taking advantage of the fact that vehicleoperators are creatures of habit. One takes the same route to the officeevery weekday, or at least one of perhaps two alternative routes whichthe system would quickly learn. On weekends, local or longer trips arefrequently repeated, at least over a period of time. A self learningsystem would also learn that the operator almost always slows and getsoff a freeway on the same downward directed off ramp to a downhillstreet, whereby the system would automatically save energy storagecapability for storing the energy of slowing before and during thedowngrade. Such a system not only would quickly learn the elevationversus position of the roads one normally travels, but would also learnhow that driver uses those roads, which could be as beneficial orperhaps more beneficial that simply using road elevation versus positioninformation. Such information might be parsed as weekday and weekendinformation, or broken down to day and time of day, or self adaptingtime breakdown dependent on the habits of the vehicle operator.

By way of example, if one approaches an upgrade that is followed by asteep upgrade, a simple database based system would save as much storedenergy during the upgrade as possible for use for the steep upgrade.However a self learning system would know that the vehicle operatoralways stops for a while just before the steep upgrade and then turnsaround to go back. The self learning system would learn this pattern soas to not have significant stored energy when the base of the steepupgrade is reached, to have capacity for energy storage as the vehiclereturns down the upgrade. Within limits, the greater the energy storagecapability, the greater the efficiency gain a system could achieve.Certainly from a cost benefit viewpoint, GPS units are now relativelyinexpensive, and in fact are being included in increasing numbers of newvehicles as part of current day navigation systems anyway. Also memorystorage and computing power are current relatively inexpensive and arefurther increasing in capability and decreasing in cost as time goes on.Such a system can interface with the engine controller, so that theprimary cost of implementation is the software development cost, whichis a one-time cost.

So far, this aspect of the present invention has been described withrespect to use with the present invention with high pressure air storagefor the energy storage, though obviously other forms of propulsion andenergy storage may be used as desired. By way of example, the presentinvention may be advantageously used with other energy storagefacilities, such a battery storage, flywheel energy storage, etc. inhybrid powered vehicles. Actually, as stated before, generally the moreenergy storage provided, the more efficient such a system becomes, asits look-ahead capability simply increases.

In the foregoing description, a self learning system was described as analternative to a database based system. Actually both may be usedtogether, as each has certain unique capabilities the other does not, sothat the combination of the two systems will be more efficient thaneither alone. Further, a self learning system may gather data which maybe collected by users of the system and collectively put together toform the database for the database system. These are mere examples ofwhat may be done, as there may be other GPS based techniques that may beused alone or in combination with these or other techniques to achievethe desired performance.

In the foregoing disclosure, reference was made to ammonia and naturalgas as examples of fuels that may be used with embodiments of theinvention. Note that these and other fuel may be used with otherembodiments disclosed herein as applicable. In that regard, unless thecontext indicates otherwise, the words injection and injector when usedin conjunction with fuels are used in the general sense to includeintroduction of fuel and device for the introduction of fuel generally.

Also, the invention illustrated in FIG. 8 and its method of operationmay be used with all embodiments, which in general will allow use ofnear stoichiometric fuel/air ratios while still limiting thetemperatures attained in the combustion chamber to less thantemperatures at which NO_(X) is formed.

Thus the present invention has a number of aspects, which aspects may bepracticed alone or in various combinations or sub-combinations, asdesired. While certain preferred embodiments of the present inventionhave been disclosed and described herein for purposes of illustrationand not for purposes of limitation, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the full breadth of the following claims.

What is claimed is:
 1. A method of operating a compression ignitionengine having at least one combustion cylinder and at least onecompression cylinder, the method comprising: a) taking air into thecompression cylinder during an intake stroke of the compressioncylinder, compressing the air in the compression cylinder during acompression stroke and delivering the compressed air to an air rail; andb) coupling the air rail to the combustion cylinder at or near beginningof an intake stroke of the combustion cylinder, and decoupling the airrail from the combustion cylinder before a pressure in the combustioncylinder exceeds a pressure in the air rail.
 2. The method of claim 1,further comprising: c) compressing the air in the combustion cylinder toobtain ignition of a fuel in the air in the combustion cylinder at ornear the end of a compression stroke of the combustion cylinder; d)executing a power stroke followed by another intake stroke in thecombustion cylinder; and e) repeating a) through d).
 3. The method ofclaim 2, further comprising: injecting a liquid fuel into the combustioncylinder during the intake stroke of the combustion cylinder of b) or atleast early in the compression stroke of the combustion cylinder of c)to provide the fuel in the air in the combustion cylinder in c).
 4. Themethod of claim 2, further comprising: opening an engine valve toincrease a volume of the combustion cylinder after the ignition andbefore the combustion cylinder reaches a temperature at which NO_(x) isgenerated.
 5. The method of claim 4, further comprising: sensingcompression ignition of fuel in the combustion cylinder and pistonposition when compression ignition occurs, and adjusting timing ofoperation of the engine valve, cycle to cycle, to maintain compressionignition at or near a top dead center position of the respective piston.6. The method of claim 5, wherein adjusting the timing of operation ofthe engine valve comprises controlling the engine valve through anelectronically controlled, hydraulically operated engine valve actuationsystem.
 7. The method of claim 2, further comprising: sensingcompression ignition of fuel in the combustion cylinder and pistonposition when compression ignition occurs, and adjusting timing ofoperation of at least one engine valve, cycle to cycle, to maintaincompression ignition at or near a top dead center position of therespective piston.
 8. The method of claim 2, further comprising: sensingcompression ignition of fuel in the combustion cylinder and pistonposition when compression ignition cylinder occurs, and adjusting timingof operation of at least one engine valve in the compression cylinder,cycle to cycle, to maintain compression ignition at or near a top deadcenter position of the respective piston.
 9. The method of claim 2,further comprising: coupling an air tank to the air rail; and storingcompressed air in the air tank when using the compression ignitionengine as a brake.
 10. The method of claim 2, wherein the fuel isammonia or natural gas.
 11. The method of claim 2, further comprising:storing energy in the compressed air in an air storage tank.
 12. Themethod of claim 1, further comprising: injecting a gaseous fuel into anintake manifold that delivers the air into the compression cylinder ina) or into the compression cylinder during the intake stroke of thecompression cylinder of a).
 13. The method of claim 1, furthercomprising: supercharging the air in an intake manifold, wherein the airis taken into the compression cylinder from the intake manifold.
 14. Themethod of claim 1, further comprising injecting fuel into an intakemanifold that takes the air into the compression cylinder, or into thecompression cylinder during the intake stroke of the compressioncylinder.
 15. The method of claim 1, wherein the at least one combustioncylinder and the at least one compression cylinder (i) all act ascompression cylinders, (ii) all act as combustion cylinders, or (iii)each cylinder sometimes acts as a compression cylinder and sometimesacts as a combustion cylinder.
 16. A method of operating a compressionignition engine comprising at least one compression cylinder and atleast one combustion cylinder, the method comprising: a) taking fuel andair into the compression cylinder during an intake stroke of thecompression cylinder, compressing the fuel and air in the compressioncylinder during a compression stroke of the compression cylinder, anddelivering the compressed fuel and air to an air rail; b) coupling theair rail to the combustion cylinder at or near the beginning of acompression stroke of the combustion cylinder and decoupling the airrail from the combustion cylinder before a pressure in the combustioncylinder exceeds a pressure in the air rail; and c) further compressingthe fuel and air in the combustion cylinder to obtain ignition of fuelin the air in the combustion cylinder at or near the end of thecompression stroke of the combustion cylinder.
 17. The method of claim16, further comprising: d) executing a power stroke followed by anexhaust stroke in the combustion cylinder; and e) repeating a) throughd).
 18. The method of claim 17, further comprising: opening and thenclosing an exhaust valve during the intake stroke of the combustioncylinder to recirculate some exhaust gas.
 19. The method of claim 17,further comprising: storing energy in the compressed air in an airstorage tank.
 20. The method of claim 17, further comprising:supercharging the intake air.